Electrophotographic material and process employing metal resinates



United States Patent 3,373,020 ELECTROPHOTOGRAPHIC MATERIAL AND PROCESS EMPLOYING METAL RESINATES Martha Tomanek, Wiesbaden-Biebrich, Germany, assignor, by mesne assignments, to Azoplate Corporation, Murray Hill, N.J., a corporation of New Jersey No Drawing. Filed Dec. 16, 1963, Ser. No. 330,602 Claims priority, application Germany, Dec. 18, 1962, K 48,510 31 Claims. (Cl. 96-1.5)

ABSTRACT OF THE DISCLOSURE The present invention relates to an electrophotographic material comprising a conductive carrier and a photoconductive insulating layer applied thereto, the latter comprising metal resinates or such compounds in combination with additives. The term metal resinates as used herein means salt-like compounds of metals and resin acids.

As is known, the electrophotographic process comprises electrostatically charging, in the absence of actinic light, a photoconductive insulating layer comprising a photoconductor compound and then exposing the charged area to light under a master, whereby the charge leaks away in the exposed areas. The latent electrostatic image thus obtained is made visible by treatment .with a toner and, if necessary, fixed.

Photoconductive insulating layers have been proposed containing inorganic or low molecular weight organic photoconductor materials. Such materials include e.g. sulfur, zinc oxide, anthracene, anthraquinone, oxazoles ortriphenylmethane. If these photoconductors are used, they must be applied to the carrier in combination withbinders in order to form a layer suitable for practical purposes. If no binders are used, the photoconductor substances do not adhere at all or only insufiiciently adhere to the carrier, because of their amorphous or crystalline structure, and, because of their non-uniform distribution, non-uni! form images are obtained. Thus, these images are not very suitable for storage and for reproduction. purposes.

It is also known to use high molecular weightv compounds, e.g. polyacrylic acid and its derivatives, for this purpose. Without the admixture of film-forming substances, these high molecular weight compounds also can be used for reproduction with certain restrictions only. They have an adverse influence on the image production because of their tendency to turn yellow and form a nonuniform undulating surface. Apart from this, the number of solvents therefor is very limited so that difiiculties are encountered in producing the coating solution. Further, their photoconductor properties are not entirely satisfactory.

'The electrophotographic material of the present invention enables a homogeneous photoconductor layer comprising a uniform chemical substance of resinous character to be used for reproduction purposes. The carrier advantageously can be coated with the layer in one coating step without previous mechanical mixing of the various ingredients. The metalresinates which are used in the present invention are readily soluble in all conventional solvents so that the selection and concentration of the solvents used for the production of the coating solution may be widely varied. The surface of the photoconductive layer is smooth and does not show any disturbing tendency to turn yellow, which impairs the usefulness of the layer Due to theuniform structure of the layer, an equal and uniform photoconductivity is elfected at all points of the layer, whereby an excellent image with high marginal sharpness isobtained. The material of the present invention preferably is used for the production of printing cadmium, chromium,

3,373,020 Patented-Mar. 12,. 1968 2 plates. The photoconductive compounds give excellent re-- sults also in combination with resinous binders, since they comprise an inorganic and an organic component.

The term metal resinates used in the present invention means salt-like compounds of metals and resin acids. Such compounds sometimes are called resin soaps or resin acid salts. The resinates are known. They can be obtained e.g. by reacting metal salts with resin acids in solvents, if necessary while heating, or by melting the two components together. Generally, these compounds are not uniform as they are commercially produced and used. However, it is possible to obtain well defined compounds by using stoichiometric quantities of the stated reaction components. Both types of compounds may be used in the present invention. Methods for the production thereof are described e.g. in Kunststoff, Lack-und Gummianalyse by D. Hummel, Carl Hauser-Verlag, Munich (1958), page 119 et seq. The literature cited further describes a method for the production of metal resinates by melting metal oxides and metal hydroxides together with resin acids.

The term resin acid components as used in the present case is meant to include e.g. low molecular weight products which may be isolated from vegetable resins ac cording to known procedures. Resins with an extraordinarily high acid content are found in the secretions of conifers, e.g. pines and firs. These natural resin acids are mostly mixtures of isomeric monocarboxylic acids in the case of conifers, e.g. pimaric acid or abietic acid having the formula 0 1-1 0 Other Well known resins which may be used with advantage in the present invention are e.g. aromatic acids which are found in the copal resins, such as agathenediocic acid C H O illuric acid C H O podocarpic acid C17H2203, fusion point 188 C., elemic acid C H O sumaresinolicacid C H O and siaresinolic-acid C30H4g04. Generally, these acids have melting points between 130 and 300 C. Some of themmay be easily separated. As far as their chemical constitution is known, the resin acids may also be synthetically produced.

Metallic compounds, e.g. metal salts or metal oxides which may be used in the present case for the production of metal resinates, are derivatives of metals of the entire Periodic System, e.g.- sodium, potassium, magnesium, calcium, strontium, barium, aluminum, tin, lead, antimony, bismuth, iron, cerium, cobalt, nickel, copper, silver, zinc,

molybdenum, manganese or mixtures of such metals.

A bromic acid, hydrofluoric acid, hydroboric acid or the sulfuric or phosphoric acids. Examples of the metal resinates used in the present invention are listed in LackrohstolT-Tabellen by Karsten, 2nd edition, Curt R. Vincentz Verlag, Hannover (1959), pages 27, 28, 217 and 218.

The most common representatives of this group are Zinc resinates containing 4 to 8 percent by weight of zinc and, cium. A material of this kind is, e.g. Erkazit Hartharz 44, having a melting point between 130 and 150 C., a calculated acid number of 30 and a color value of 8.5 to 9.5. Other suitable compounds are, e.g. Erkazit Magnesium- Hartharz V 112, having a melting point of 120 to 140 C. and an acid number below 50, or a hardened rosin with a melting point of 115 to 125 C., an acid number of 70 to and a color value of 80 to furthermore metal resinates such as cerium resinate containing 8 percent cerium and ob'tained'from a mixture of resin acids isolated from copal resin; as well as metal resinates with this resin acid mixture which contain 33 percent by weight if desired, about 4 to 10 percent by weight of cal-,

t. of manganese and 13.1 percent by weight of lead, or 8 percent by weight of copper, or 28.6 percent by weight of lead, or 1.8 percent by weight of cobalt, 0.45 percent by weight of manganese, 1.1 percent by weight of barium, and 0.7 percent by weight of Zinc are suitable.

Other metal resinates are described in The Technology of Natural Resins by C. L. Mantell, New York, Wiley (1942); Naturharze, Terpentinol, Tallol, by W. sandermann, Springer-Verlag, Berlin (1960), and in Chemie-Lexikon by H. Rompp, th edition, Franckshe Verlagschuchhandlung, Stuttgart (1962), pages 2085/ 2086.

The use of metal resinates alone as photoconductive insulating layers gives, as stated above, good results. However, the properties of the layers, i.e. the lightsensitivity and the mechanical properties thereof, may be improved by additives. Such additives are e.g. inorganic and organic photoconductors, sensitizers, activators, pigments, film-forming substances, and stabilizers. Photoconductors which may be added to the layers of the invention are inorganic and organic photoconductive substances. Good results are obtained if photoconductive zinc oxide and organic compounds such as oxadiazoles, imidazoles, triazoles, oxazoles, thiazoles, and imidazolones are added.

By the addition of sensitizers, the spectral sensitivity of the photoconductive layers may be shifted further into the visible range so that the exposure times may be shortened while good results are still obtained. Small additions such as 0.001 percent by weight have shown good effects. Such sensitizers, most of which are dyestuffs, are described e.g. in Belgian Patent No. 558,078.

It has also proved advantageous to add minor amounts of activators to the layers of the present invention. Such compounds are described in German Patents Nos. 1,068,- 115, and 1,111,935. It was found that dialkylarninobenzoic acids such as diethylamino-benzoic acid, ethylpropylamino-benzoic acid and dichloro-benzoic acid, or 2,3- dichloro-naphthoquinone, chloraniline, or anthraquinone are particularly suitable.

Suitable pigments which, if desired, may be added in minor amounts to obtain special layer effects are titanium dioxide, aluminum oxide and non-photoconductive zinc oxide.

If film-forming substances are added to improve the layer quality, they may be resins such as: balsam resin, colophony, shellac, and synthetic resins, such as phenolic resins modified with colophony, and other resins with a higher proportion of colophony, coumarone resins, in dene resins and the resins within the collective term of lacquer resins. As shown by the iunstoiftaschenbuch by saechtlingZebrowski, 11th edition (1955), pages 212 et seq., these lacquer resins include modified natural substances such as cellulose ethers, polymers such as vinyl polymers, e.g. polyvinyl chloride, polyvinylidene chloide, polyvinyl acetate, polyvinyl acetals, polyvinyl ether, copolymers of vinyl chloride, vinyl acetate, and maleic acid, polyacrylic ester, polymethacrylic ester, polystyrene and copolymers, e.g. of styrene and maleic anhydride, polycondensates, e.g. polyesters such as phthalate resins, terephthalic acid and isophthalic acid-ethyleneglycolpolyester, maleinate resins, maleic acid/colophony/mixed esters of higher alcohols, phenolformaldehyde resins, particularly condensates of phenol and formaldehyde modified with colophony, urea-formaldehyde resin, condensates of melamine and formaldehyde, aldehyde resins, ketone resins, xylene-formaldehyde resins, polyamides, polyurethanes, and polyolefins such as low molecular weight polyethylene, polypropylene, polyisobutylene, and chlorinated rubber may also be used for this purpose.

If the compounds of the present invention are used in admixture with the above resins, the ratio of resin to photoconductor may vary within a wide range. Mixtures of 2 parts by weight of resin and 1 part by weight of photoconductor to mixtures containing 2 parts by weight of photoconductor per part by weight of resin are preferred.

Stabilizers which may be added are e.g. zinc chloride, naphthalene-1,3,6-trisulfonic acid or other compounds conventionally used for this purpose.

The overall quantity of the additives to be added should be kept low, e.g. normally at a maximum of 40 percent by weight, however, a few percent will be enough for special purposes.

As a carrier for the photoconductive layers of metal resinates, there may be used all suitable supports known for this purpose, particularly metal and paper. If paper is used as a carrier, it preferably should be pretreated to prevent the penetration of the coating solution. Foils provided with a metal layer, e.g. of aluminum, by lamination or vacuum-deposition are well suited for this purpose.

For the production of the electrophotographic material, the metal resinates are preferably dissolved in organic solvents such as benzene, acetone, methylene chloride, ethylene glycolmonomethylether or mixtures thereof and the carrier is coated in a conventional manner, e.g'. by dipping, spraying, brushing or roller application. The layer is then dried whereupon a uniform, homogeneous, transparent, mostly uncolored photoelectrically conductive layer is obtained.

For the preparation of copies using the electrophotographic copying material of the invention, the photoelectrically conductive insulating layer of the invention is charged, e.g. by a corona discharge from a charging device maintained at 6,000 to 7,000 volts. Then, the electrophotographic copying material is exposed under a master, or by episcopic or diascopic projection of a master, so that an electrostatic image corresponding to the master is obtained. This invisible image is developed by contacting it in known manner with a developer comprising a carrier and a toner. The developer may also comprise a resin or a pigment which is suspended in a dielectric liquid. The image made visible in this way is fixed, e.g. by heating with an infrared radiator to about to 170 C., preferably to C., or by treatment with solvent vapors such as trichloroethylene, carbon tetrachloride or ethyl alcohol or with steam. Thus, images are obtained corresponding to the masters used and having excellent contrast effect.

A particularly preferred field of application of the material of the present invention is in the printing art, by transforming the images obtained by electrophotographic methods and, after fixing, into printing plates. The excellent solubility of the metal resinates in numerous solvents is of advantage since a particularly easy and thorough decoating of the non-printing areas is facilitated. Further, the metal resinates have an excellent adhesion to metallic supports which particularly increases the resistance to abrasion of the printing plate during the printing process. Thus longer runs with uniform quality are obtained.

Such a transformation of a fixed electrophotographic image may be effected by rubbing the carrier material, e.g. paper or metal, with a solvent for the photoelectrically conductive layer, e.g. with alcohol, acetic acid or caustic soda solution, then rinsing with water and contacting it in known manner with greasy ink. Thus, printing plates are obtained, which may be set up in an offset machine and used for printing.

If transparent carrier materials are used, the electrophotographic images may also be used as masters for producing further copies on any light-sensitive layer. Further, images may be produced by the reflex process if transparent carrier substances are used for the photoconductive layers of the present invention. The electrophotographic material has the advantage that it may be charged positively as well as negatively, so that by merely reversing the poles, positive images may be obtained from negative as well as from positive masters, with the same developer.

If e.g. the layer is charged negatively and exposed under a positive master, positive images are obtained if a developer is used containing a positively charged toner. The positively charged toner is deposited in the unexposed, negatively charged areas.

If the layer is positively charged, positive copies may be obtained under the same conditions from negative masters. The positive toner in this case is repelled by the unexposed positively charged areas and is deposited in the exposed, discharged areas.

The invention will be further illustrated by reference to the following specific examples:

Example 1 2 parts by weight of zinc resinate, i.e. Erkazit Zinkharz 165, having a fusion point between 150 and 170 C., are dissolved in 30 parts by weight of toluene, and 0.004 part by weight of crystal violet, dissolved in 0.5 part by volume of methanol, is added. The solution is applied to paper, the surface of which was pretreated to prevent the penetration of organic solvents, and then dried. The paper coated in this way is negatively charged by means of a corona discharge, exposed under a positive master with a 500 watt bulb, and contacted in known manner with a developer comprising a carrier and a toner. Suitable carriers are tiny glass balls, iron powder, and other inorganic materials. The toner comprises a mixture of a resin and carbon black or colored resins having an average particle size of l to 100/l.- An image corresponding to the master is obtained which is fixed by slight heating and shows excellent contrast effect.

Example 2 1 part by weight of a lead resinate, i.e. Bleiresinat No. 152, which has a lead content of 28.6 percent by weight, 0.05 part by weight of chloranil, and 0.005 part by weight of brillant green are dissolved in 15 parts by volume of chloroform, and the solution is applied to aluminumlaminated paper. After evaporation of the solvent, a layer remains which --firmly adheres to the aluminum surface. After negative charging by means of a corona discharge, the paper is exposed for one minute under a positive master, using a 500 watt bulb at a distance of 30 cm. Then, a developer powder as employed in Example 1 is applied. An image corresponding to the master is obtained which is fixed by means of trichloroethylene vapors.

Example 3 In 100 parts by volume of ethyleneglycol monomethylother there are dissolved parts by weight of an iron resinate, i.e. a mixture of 90 percent by weight of an iron salt of abietic acid and 10 percent by Weight of an iron salt of pimaric acid, 2 parts by weight of ethylpropylaminobenzoic acid and 0.01 part by weight of Rhodamine B extra, and the solution is applied to a mechanically roughened, brushed aluminum foil, the brushing effect having a mean depth of 4 to 5;. After evaporation of the solvent, a layer with a thickness of 4a remains which adheres firmly to the surface of the foil. The electrocopying material thus obtained is negatively charged by a corona discharge and then exposed in the cassette of a reproduction camera. A book page printed on both sides serves as the master. The layers allow a uniform development of surfaces of size DIN A 4 by means of a developer powder without using magnetic brushes.

As developer powder there may be used e.g., a toner mixture consisting of kieselguhr and a toner comprising a low melting point mixture of polystyrene and colo phony to which carbon black is added and desirably also spirit-soluble Nigrosin as an organic dyestuff.

The components of the toner are melted together, subsequently milled, and air sifted since a uni-form grain size is preferable for the production of images. A fraction containing a toner with grain sizes from 5" to 101w is very suitable. For screen work, a toner with a grain size from 0.5 to 2 is best employed. After powdering the latent electrophotographic image with the toner mixture, the image is fixed by heating to 150 to 170 C. for 30 seconds.

The electrophotographic image thus obtained may be transformed to a printing plate by swabbing it with a solution containing 40 percent by weight of methanol, 10 percent by weight of glycerine, 45 percent by weight of glycol, and 5 percent by weight of sodium silicate. The areas of the layer not covered by the toner are dissolved away and rendered hydrophilic whereas the printing or image areas accept greasy ink so that, after mounting the printing plate thus obtained in an offset machine, printing can be performed.

Example 4 2 parts by weight of the antimony salt of dehydroabietic acid, isolated from colophony, 0.15 part by weight of dichloro-acetic acid and 0.006 part by weight of Eosin S are dissolved in 30 parts by weight of methylene chloride, and the solution is applied to a paper sheet which is impermeable to solvents. After evaporation of the solvent, the remaining layer adheres firmly to the paper surface. The further procedure for the preparation of an image is as described in Example 1 and, when a positive master is used, a positive image is obtained which is also fixed as in Example 1.

Example 5 The process of Example 1 is followed with the exception that the zinc resinate is replaced by a calcium resinate, i.e. Crayvallac 571, containing 5 percent calcium. The dried layer is charged positively and exposed under a negative master. After developing and fixing according to Example 1, a positive copy is obtained.

Example 6 2.5 parts by weight of a cobalt resinate containing 7.3 percent by weight of cobalt, 2.5 parts by weight of a magnesium resinate, 0.3 part by weight of diethylaminobenzoic acid and 0.006 part by weight of rose bengal are dissolved in 40 parts by volume of benzene and the solution is applied to a brushed aluminum foil. After evaporation of the solvent, a layer remains which adheres firmly to the surface of the foil. Further procedure is as in Example 1 and an image corresponding to the master is obtained on the aluminum surface which, after powdering with a developer as described in Example 1, is fixed by heating. The aluminum foil provided with the image can be converted into a printing plate by swabbing the image side of the aluminum foil with percent alcohol, rinsing with water and rubbing with greasy ink and 1 percent phosphoric acid. A printingplate is obtained corresponding to the master used which, after fixing, may be used for printing.

Example 7 25 parts by weight of zinc resinate, having a fusion point of to C., 3 parts by weight of anthraquinone and 0.01 part by weight of patent blue AE are dissolved in a mixture of 50 parts by volume of benzene and 50 parts by volume of chloroform. The resulting solution is applied to a paper sheet which is treated to prevent the penetration of solvents. Direct images are produced on the paper following the procedure described in Example 1.

Example 8 2 parts by weight of manganese resinate, containing 3 percent by weight of manganese, 0.01 part by weight of ion-trichloride and 0.003 part by weight of methyl violet are dissolved in 20 parts by volume of trichloroethylene and the solution is applied to aluminum-laminated paper. After evaporation of the solvent, a layer remains which adheres firmly to the aluminum surface. The layer is positively charged by a corona discharge and exposed under a positive master. The developer used comprises a mixture of a colored resin/carbon black mixture and resin-coated glass balls. A positive copy is obtained.

Example 9 1 part by weight of cerium resinate, containing 8 percent by weight of cerium, 1 part by weight of a cobaltbarium-Zinc resinate, and 0.2 part by weight of 1,4-toluquinone are dissolved in 30 parts by volume of toluene and 0.005 part by weight of methylene blue in 1 part by volume of methanol is added. For the remainder of the process, the procedure of Example is followed.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. An electrophotographic material comprising a conductive support having a photoconductive insulating layer thereon, the latter comprising a metal resinate.

2. An electrophotograpliic material according to claim 1 in which the resinate is zinc resinate.

3. An electrophotographic material according to claim 1 in which the resinate is lead resinate.

4. An electrophotographic material according to claim 1 in which the resinate is iron resinate.

5. An electrophotographic material according to claim 1 in which the resinate is antimony resinate.

6. An electrophotographic material according to claim 1 in which the resinate is calcium resinate.

7. An electrophotographic material according to claim 1 in which the resinate is cobalt resinate.

8. An electrophotographic material according to claim 1 in which the resinate is manganese resinate.

9. An electrophotographic material according to claim 1 in which the resinate is cerium resinate.

10. An electrophotographic material according to claim 1 in which the photocond-uctive layer includes a different photoconductor.

11. An electrophotographic material according to claim 1 in which the photoconductive layer includes a sensitizer.

12. An electrophotographic material according to claim 1 in which the photoconductive layer includes an activator.

13. An electrophotographic material according to claim 1 in which the photoconductive layer includes a pigment.

14. An electrophotographic material according to claim 1 in which the photoconductive layer includes a filmfor-ming substance.

15. An electrophotographic material according to claim 1 in which the photoconductive layer includes a stabilizer.

16. A photographic reproduction process which comprises exposing a supported, electrostatically charged, photoconductive insulating layerto light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising a metal resinate.

17. A process according to claim 16 in which the resimate is zinc resinate.

18. A process according to claim 16 in which the resinate is lead resinate.

19. A process according to claim resinate is iron resinate.

20. A process according to resinate is antimony resinate.

21. A process according to resinate is calcium resinate.

22. A process according to resinate is cobalt resinate.

23. A process according to resinte is manganese resinate.

24. A process according to claim resinate is cerium resinate.

25. A process according to claim 16 in which the photoconductive layer includes a different photoconductor.

26. A process according to claim 16 in which the photoconcluctive layer includes a sensitizer.

27. A process according to claim 16 in which the photoconductive layer includes an activator.

16' in which the claim 16 in which the claim 16 in which the claim 16 in which the claim 16 in which the 16 in which the 28. A process according to claim 16 in which the photoconductive layer includes a pigment.

29. A process according to claim 16 in which the photoconductive layer includes a film-forming substance. 30. A process according to claim 16 in which the photoconductive layer includes a stabilizer.

31. A process according to claim 16 in which the image is fixed and the layer is treated to decoat it and liydrophilize the support in the image-free areas.

References Cited UNITED STATES PATENTS 2,562,020 7/1951 Darlington 260- X 2,800,559 7/1957 Ubbelohde 96-1. 5 X 2,907,674 10/1959 Metcalfe et al 96-1 X 3,025,180 3/1962 Dalton l1736.7 3,037,938 6/ 1962 Amans 252-3013. 3,114,633 12/1963 Schlesinger 96-1.6 3,138,458 6/1964 Kimble et al. 96--l.8 3,236,640 2/1966 Tomanek et al. 96--l.6 3,287,123 11/1966 Hoegl 961.5

OTHER REFERENCES Amick: Review of Electrofax Behavior, RCA Revie (December 1959), pp. 763-769.

NORMAN G. TORCHIN, Primary Examiner.

C. E. VAN HORN, Assistant Examiner. 

